About the Reynolds Stress Model input parameter of OpenFOAM in 2D turbulent flow.
Hello everyone, this is watermelon, a new FOAMer.
When I used the LRR model in OpenFOAM v9, I found that the input parameter of R is a symmetric tensor. I think when i use LRR to calculate the 2D turbulent flow problem, the component Rzz need to be zero. But when I check my results, i found the component Rzz also has been calculated in 2D turbulent flow, why? Any suggestion is helpful, thank you! Best regards, watermelon |
Turbulence is a 3D phenomenon ... hence even if you zero out one of the normal stresses, the pressure strain terms will repartition the turbulence energy amongst the different Reynolds stresses, including the one that you zero'd out.
Your mean flow may be two dimensional (e.g. a planar shear flow), with zero mean flow in the third direction, but the turbulence will always be three dimensional. |
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Yes, you are right, turbulent flow is 3D. What i do not understand is when i calculate a 2D case in LRR, the component of Reynolds Stress in ZZ (Rzz) is not zero. Because i think in 2D case, the Reynolds Stress should be : Rxx, Rxy, Ryx and Ryy. But when i use the LRR to calculate the 2D case, i found Rzz also be calculated, but the Rxz, Ryz, Rzx, Rzy are not be calculated. So why the Rzz be calculated in 2D case? |
Umm ... not sure how I can say this differently, my friend. Rzz should NOT be zero, even in a 2D case.
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Actually, i think when i calculate the 2D case, only the X and Y direction should be calculated. But i found OpenFOAM and Fluent are also have been calculate the Rzz when i use LRR model. I do not understand how the Rzz was calculated in a 2D case, maybe i should to get more knowledge about turbulence. Thanks again. Yours. |
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Nope. Last time of saying this. Even in a "2D case", as I explained above, the turbulence remains 3D. So the turbulence energy is the sum of ALL 3 normal stresses, and Rzz = w'w' is not zero.
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Ok, thanks a lot~~:D
Wish you good health and success in your career. Best Regards. |
OK, thank you guys.
I think I have known this problem. In Turbulent Flows, which is written by Pope, in section 4.2, prof. Pope has interpret the 2D case in turbulent flow, and the Reynolds Stress is , this is the 2D-3C (two-dimensional, 3 components) case. And what i have suppose the 2D case, the Reynolds Stress is :, this is the 2D-2C (two-dimensional, 2 components) case, and the 2D-2C is the "upper boundary" of the Lumley triangle. So, the 2D-2C is a special case of 2D-3C, and 2D-2C is usually in the near-wall turbulence condition (Pope Chapter 9). And I also derived the second-order equation in 2D case, the can be calculated. Thanks! Best Regards, watermelon |
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